Stereochemical Tailoring of Nickel-based Electrocatalysts for Hydrogen Evolution Reaction

The search for alternative non-noble transition metal catalysts able to evolve hydrogen has been the focus of intense research. Molecular complexes bearing redox-active ligands have been reported as efficient electrocatalysts for hydrogen evolution reaction (HER). This study showcases a new family of nickel-thiosemicarbazone complexes displaying significant activity for HER in DMF solvent using trifluoracetic acid as proton source. Following previous works in our group, the ligand was stereochemically tailored, placing methoxy groups at different locations and considering various combinations of positions. Three complexes within the series were shown to outperform the parent catalyst bearing the methoxy group in para position. Overall, the nickel catalyst having the chemical substituent in meta position displays the best catalytic performances while having the lowest overpotential. These results support that ligand stereochemical tailoring in metal complexes improves electrocatalytic HER and suggest that ligand tuning is a promising direction to enhance catalyst performances. A new series of nickel-thiosemicarbazone complexes was synthesized with the methoxy group placed in different positions on the phenyl ring. Their ability to promote electrocatalytic proton reduction into hydrogen was investigated. The meta-substituted complex, NiTSC-(m)-OCH3, outperformed all other tested complexes with a greatly increased TOF of 676.9 s-1 compared to the reference catalyst, NiTSC-(p)-OCH3, with a TOF of 90 s-1. image